1. Field of the Invention
The present invention relates to a radio LSI device which selects one channel from a plurality of radio channels to perform radio communication and particularly to a radio LSI device which performs channel selection according to the detection of an interfering wave. The present invention also relates to an interfering wave detecting circuit for detecting the interfering wave.
2. Description of the Related Art
FIG. 1 of the accompanying drawings shows an ordinary way of exchanging signals between a television set 1 and a remote controller 2 associated with the television set 1. The television set or TV set 1 is an apparatus that reproduces usual terrestrial or satellite, analog or digital broadcasting and has a remote control transceiver 3. The remote control transceiver 3 has specifications that conform to the remote controller 2. The remote control transceiver 3 performs the switching of broadcast channels and/or the volume adjustment of the TV set 1 according to the content of a control signal supplied from the remote controller 2. The remote controller 2 has a radio LSI device that selects one of a plurality of radio channels to perform radio communication. The remote controller 2 generates and transmits a control signal, according to a remote control button operation made by an operator, to the TV set 1 via the selected channel.
The procedure of exchanging signals in FIG. 1 will be described. First, in response to the turning on of the TV set 1, the remote control transceiver 3 is activated, and the TV set 1 waits until a control signal arrives. Meanwhile, the remote controller 2 is activated in response to the power button being pressed. The remote controller 2 executes channel selection (CCA: Clear Channel Assessment) and determines the presence/absence of a radio wave on the selected channel. If a radio wave is present on the channel, the remote controller 2 performs channel selection again a certain time (i.e., delay time) later. The delay time is decided by random numbers or the like. This operation is repeated until the channel becomes vacant. When a radio wave is not present on the channel, the remote controller 2 transmits a control signal corresponding to the operator's remote control button operation over the selected channel and waits.
Upon receiving a control signal from the remote controller 2, the TV set 1 transmits an Ack (acknowledgement) signal acknowledging successful signal reception. The TV set 1 performs an operation (such as volume adjustment) according to the control signal and waits for the next control signal. Meanwhile, when having received the Ack signal from the TV set 1, the remote controller 2 finishes this remote control operation.
The lower part of FIG. 1 depicts a case where an interfering wave is present. If an interfering wave is present when the remote controller 2 transmits a control signal, the TV set 1 will not transmit an Ack signal in response to this control signal, or even if the TV set 1 transmits the Ack signal, the Ack signal does not reach the remote controller 2. If an Ack signal does not arrive at the remote controller 2 even after a predetermined time has passed, the remote controller 2 gives up transmitting the control signal over this channel and performs channel selection again to switch to another channel. Such phenomenon causes an operating delay of the remote controller 2 and also an increase in power consumption of the battery incorporated in the remote controller 2.
Japanese Patent Application Kokai (Laid-Open) No. 2000-069565 discloses a technique for avoiding a reduction in throughput due to the switching of radio channels. Paragraph 0023 and FIG. 2 of Japanese Patent Application Kokai No. 2000-069565 describe that if it is determined that the result of a first radio channel electric field intensity measurement and the result of a second radio channel electric field intensity measurement after a predetermined time (a set count time) has passed from the first measurement both exceed a reference value, then the switching of radio channels is performed.